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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

2FHL: The Second Catalog of Hard Fermi-LAT Sources

We present a catalog of sources detected above 50 GeV by the Fermi-Large Area Telescope (LAT) in 80 months of data. The newly delivered Pass 8 event-level analysis allows the detection and characterization of sources in the 50 GeV–2TeV energy range. In this energy band, Fermi - LAT has detected 360 sources, which constitute the second catalog of hard Fermi -LAT sources (2FHL). The improved angular resolution enables the precise localization of point sources (~1.'7 radius at 68 % C. L.) and the detection and characterization of spatially extended sources. We find that 86% of the sources can be associated with counterparts at other wavelengths, of which the majority (75%) are active galactic nuclei and the rest (11%) are Galactic sources. Only 25% of the 2FHL sources have been previously detected by Cherenkov telescopes, implying that the 2FHL provides a reservoir of candidates to be followed up at very high energies. This work closes the energy gap between the observations performed at GeV energies by Fermi -LAT on orbit and the observations performed at higher energies by Cherenkov telescopes from the ground.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE ROLE OF KELVIN–HELMHOLTZ INSTABILITY FOR PRODUCING LOOP-TOP HARD X-RAY SOURCES IN SOLAR FLARES

We propose a model for the formation of loop-top hard X-ray (HXR) sources in solar flares through the inverse Compton mechanism, scattering the surrounding soft X-ray (SXR) photons to higher energy HXR photons. We simulate the consequences of a flare-driven energy deposit in the upper chromosphere in the impulsive phase of single loop flares. The consequent chromosphere evaporation flows from both footpoints reach speeds up to hundreds of kilometers per second, and we demonstrate how this triggers Kelvin–Helmholtz instability (KHI) in the loop top, under mildly asymmetric conditions, or more toward the loop flank for strongly asymmetric cases. The KHI vortices further fragment the magnetic topology into multiple magnetic islands and current sheets, and the hot plasma within leads to a bright loop-top SXR source region. We argue that the magnetohydrodynamic turbulence that appears at the loop apex could be an efficient accelerator of non-thermal particles, which the island structures can trap at the loop-top. These accelerated non-thermal particles can upscatter the surrounding thermal SXR photons emitted by the extremely hot evaporated plasma to HXR photons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A RECONNECTION-DRIVEN MODEL OF THE HARD X-RAY LOOP-TOP SOURCE FROM FLARE 2004 FEBRUARY 26

A compact X-class flare on 2004 February 26 showed a concentrated source of hard X-rays at the tops of the flare’s loops. This was analyzed in previous work and interpreted as plasma heated and compressed by slow magnetosonic shocks (SMSs) generated during post-reconnection retraction of the flux. That work used analytic expressions from a thin flux tube (TFT) model, which neglected many potentially important factors such as thermal conduction and chromospheric evaporation. Here we use a numerical solution of the TFT equations to produce a more comprehensive and accurate model of the same flare, including those effects previously omitted. These simulations corroborate the prior hypothesis that slow-mode shocks persist well after the retraction has ended, thus producing a compact, loop-top source instead of an elongated jet, as steady reconnection models predict. Thermal conduction leads to densities higher than analytic estimates had predicted, and evaporation enhances the density still higher, but at lower temperatures. X-ray light curves and spectra are synthesized by convolving the results from a single TFT simulation with the rate at which flux is reconnected, as measured through motion of flare ribbons, for example. These agree well with light curves observed by RHESSI and GOES and spectra from RHESSI . An image created from a superposition of TFT model runs resembles one produced from RHESSI observations. This suggests that the HXR loop-top source, at least the one observed in this flare, could be the result of SMSs produced in fast reconnection models like Petschek’s.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles

Flares close to the solar limb, where the footpoints are occulted, can reveal the spectrum and structure of the coronal looptop source in X-rays. We aim at studying the properties of the corresponding energetic electrons near their acceleration site, without footpoint contamination. To this end, a statistical study of partially occulted flares observed with Reuven Ramaty High-Energy Solar Spectroscopic Imager is presented here, covering a large part of solar cycles 23 and 24. We perform detailed spectra, imaging, and light curve analyses for 116 flares and include contextual observations from SDO and STEREO when available, providing further insights into flare emission that were previously not accessible. We find that most spectra are fitted well with a thermal component plus a broken power-law, non-thermal component. A thin-target kappa distribution model gives satisfactory fits after the addition of a thermal component. X-ray imaging reveals small spatial separation between the thermal and non-thermal components, except for a few flares with a richer coronal source structure. A comprehensive light curve analysis shows a very good correlation between the derivative of the soft X-ray flux (from GOES ) and the hard X-rays for a substantial number of flares, indicative of the Neupert effect. The results confirm that non-thermal particles are accelerated in the corona and estimated timescales support the validity of a thin-target scenario with similar magnitudes of thermal and non-thermal energy fluxes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

NuSTAR Hard X-Ray Observation of a Sub-A Class Solar Flare

We report a Nuclear Spectroscopic Telescope Array ( NuSTAR ) observation of a solar microflare, SOL2015-09-01T04. Although it was too faint to be observed by the GOES X-ray Sensor, we estimate the event to be an A0.1 class flare in brightness. This microflare, with only ∼5 counts s{sup −1} detector{sup −1} observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager ( RHESSI ), is fainter than any hard X-ray (HXR) flare in the existing literature. The microflare occurred during a solar pointing by the highly sensitive NuSTAR astrophysical observatory, which used its direct focusing optics to produce detailed HXR microflare spectra and images. The microflare exhibits HXR properties commonly observed in larger flares, including a fast rise and more gradual decay, earlier peak time with higher energy, spatial dimensions similar to the RHESSI microflares, and a high-energy excess beyond an isothermal spectral component during the impulsive phase. The microflare is small in emission measure, temperature, and energy, though not in physical size; observations are consistent with an origin via the interaction of at least two magnetic loops. We estimate the increase in thermal energy at the time of the microflare to be 2.4 × 10{sup 27} erg. The observation suggests that flares do indeed scale down to extremely small energies and retain what we customarily think of as “flare-like” properties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

NuSTAR Hard X-Ray Data and Gemini 3D Spectra Reveal Powerful AGN and Outflow Histories in Two Low-redshift Lyα Blobs

We have shown that Lyα blobs (LABs) may still exist even at z∼0.3, about seven billion years later than most other LABs known (Shirmer et al.). Their luminous Lyα and [O iii] emitters at z∼0.3 offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at z∼0.3, SDSS J0113+0106 (J0113) and SDSS J1155−0147 (J1155), comparable in size and luminosity to “B1,” one of the best-studied LABs at z≳2. Our NuSTAR hard X-ray (3–30 keV) observations reveal powerful active galactic nuclei (AGN) with L{sub 2--10keV}=(0.5--3)×10{sup 44} erg s{sup −1}. J0113 also faded by a factor of ∼5 between 2014 and 2016, emphasizing that variable AGN may cause apparent ionization deficits in LABs. Joint spectral analyses including Chandra data constrain column densities of N{sub H}=5.1{sub −3.3}{sup +3.1}×10{sup 23} cm{sup −2} (J0113) and N{sub H}=6.0{sub −1.1}{sup +1.4}×10{sup 22} cm{sup −2} (J1155). J0113 is likely buried in a torus with a narrow ionization cone, but ionizing radiation is also leaking in other directions, as revealed by our Gemini/GMOS 3D spectroscopy. The latter shows a bipolar outflow over 10 kpc, with a peculiar velocity profile that is best explained by AGN flickering. X-ray analysis of J1155 reveals a weakly absorbed AGN that may ionize over a wide solid angle, consistent with our 3D spectra. Extinction-corrected [O iii] log-luminosities are high, ∼43.6. The velocity dispersions are low, ∼100–150 km s{sup −1}, even at the AGN positions. We argue that this is a combination of high extinction hiding the turbulent gas and previous outflows that have cleared the escape paths for their successors.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

Radiation Evaluation of an Advanced 64Mb 3.3V DRAM and Insights into the Effects of Scaling on Radiation Hardness

In this paper, total ionizing dose radiation evaluations of the Micron 64 Mb 3.3 V, fast page mode DRAM and the IBM LUNA-ES 16 Mb DRAM are presented. The effects of scaling on total ionizing dose radiation hardness are studied utilizing test structures and a series of 16 Mb DRAMs with different feature sizes from the same manufacturing line. General agreement was found between the threshold voltage shifts of 16 Mb DRAM test structures and the threshold voltage measured on complete circuits using retention time measurements. Retention time measurement data from early radiation doses are shown that allow internal failure modes to be distinguished.

Radiation Hardness↗
NASA NTRS2015

Inclusion of Radiation Environment Variability in Total Dose Hardness Assurance Methodology

Variability of the space radiation environment is investigated with regard to parts categorization for total dose hardness assurance methods. It is shown that it can have a significant impact. A modified approach is developed that uses current environment models more consistently and replaces the design margin concept with one of failure probability.

radiation hardness assurance↗
NASA NTRS2016

Radiation Hardness Assurance (RHA) Guideline

Radiation Hardness Assurance (RHA) consists of all activities undertaken to ensure that the electronics and materials of a space system perform to their design specifications after exposure to the mission space environment. The subset of interests for NEPP and the REAG, are EEE parts. It is important to register that all of these undertakings are in a feedback loop and require constant iteration and updating throughout the mission life. More detail can be found in the reference materials on applicable test data for usage on parts.

Radiation Hardness Assurance (RHA)↗